Electrical oscillation generator



sept.2z,1936. N. MRUST 2,055,090

ELECTRICAL OSCILLATION GENERATOR Filed Feb. 17, 1934 'INVENTOR /VOEL /1/ R057' 'ATTORNEY Patented Sept. 22, 1936 UNITED STATES ELECTRICAL OSCILLATION GENERATOR Nol Meyer Rust, Chelmsford, England, assignor to Radio Corporation of America, a corporation of Delaware Application February 17, 1934, Serial No. l711,792 In Great Britain February 23, 1933 1 Claim.

` This invention relates to electrical oscillation generators and more particularly to valve generators of the kind wherein oscillation generation is obtained by virtue of the inherent negative re- 5 sistance properties of a thermionic valve, such, for example, as a screened grid valve. Electron discharge devices exhibiting negative resistance effects inherently, i. e., without the necessity of any external feed-back circuit, are well known and will be referred to in the present specification as negative resistance valves. The socalled screened grid valve is an example ofa negative resistance valve and, as is well known, for certain conditions of applied potential the characteristic connecting anode current (ordinates) with anode volts (abscissae) shows aV downward slope over a portion of its length, i. e., within certain limits of applied potentials the screened grid valve exhibits negative resistance 80 effects inherently.

l from said valve for applying controlling bias potentials to said valve whereby the amount of negative resistance exhibited by said valve is automatically controlled in a direction to produce sub- 35 stantial constancy of output. No claim is made to this in the present specification.

The present invention may be regarded as a development or extension of the principles set forth in my United States Patent No. 2,011,291, o supra, the objects of the present invention being to provide either a beat frequency generator arrangement or an oscillator 'succeeded by an amplifier in cascade therewith wherein despite variations (effected for the purpose of control) of 45 the frequencies of the oscillators in the case of a beat frequency generator arrangement or despite variations in the gain of an amplifying system at different frequencies and/or variations in the load fed from said amplifier system in the case of 50 an oscillator succeeded by a cascade connected ampliiier arrangement, the output amplitude shall remain substantially constant. By the term output amplitude is meant the amplitude of the voltage set up across a predetermined impedance which may be regarded for the purpose (Cl. Z50-36) of the present invention as the output impedance. According to this invention voltage set up across the output impedance of an Vamplifier preceded by a negative resistance valve oscillator or of a beat frequency generator including a nega- 5 tive resistance valve oscillator is utilized for the generation Yof controlling bias potentials which are applied to said negative resistance valve oscillator whereby the amount of negative resistance exhibited by said valve oscillator is auto- 10 matically controlled in a direction to produce substantial constancy of amplitude in the voltage set up across said output impedance.

. 4Figure 1 illustrates one embodiment wherein the invention is applied to an arrangement com- 15 prising a negative resistance valve oscillator succeeded by an amplifier system; Figure 2 shows the invention as applied to a beat frequency oscillator circuit arrangement; and Figure 3 illustrates the broad essentials of the circuit of Figure 1. Y

In Figure 1 a screened grid valve V1 is employed as a` dynatron oscillator the anode A1 of said valve being connected to the cathode K1 thereof, through a circuit including a parallel tuned circuit L1C1'n seriesV with a resistance R1 and an anode battery B1. The positive terminal of thev anode battery is connected to the negative terminal of an additional battery B2 Whose positive terminal is connected to the screen grid SG 3o of the valve V1. A condenser C2 is connected between the cathode K1 of the valveand the tuned circuit end of the resistance R1, and the control grid G1 of the valve is connected through a preferably adjustable source B3 of bias potential and 35 a capacity shunted resistance R2 to the cathode of the valve. The control grid end of the condenser shunted resistance R2 is connected to the cathode K2 of a valve arrangement V2 which, for the sake of brevity, will be herein referred to as a double-diode-triode, said double-diode-triode havingan indirectly heated cathode whose heater H is anchored in potential by being connected to the cathode K1 of the screened grid Valve V1. The double-diode-triode consists of the heater H, the indirectly heated cathode K2 heated thereby, a pair of diode anodes D1, D2, which cooperate with said indirectly heated cathodeto constitute a full wave. rectiiier, a control grid G2 and what is termed a valve anode `A2, the 50 control grid G2 and the valve anode A2 also cooperating with the indirectly heated cathode K2 after the manner of an ordinary thermionic valve. The valve anode A2 is connected through a suitable indicating meter A to the positive terminal of the high tension source B2 and the diode anodes D1, D2 are connected to the opposite ends of an inductance L2 herein termed the input inductance (this inductance is the secondary winding of an input transformer T) whose center point is connected through a suitable adjustable source of bias potential B4 to the grid G2 of the double-diodetriode. The control grid G2 of the double-diodetriode is connected through a further resistance.,

the cathode K2 R3 shunted by a condenser Ca to thereof. l

r)The tuned circuit LiCi in the anode circuit of the screened grid valve V1 isjcoupled to an amplifying system AS whose output sets up voltage.

will kbe substantially constant notwithstanding thatl the said impedance,i. e. the load, may vary and/or the gain of the amplifying system may Vary, for example, be different at different values of `workingA frequency. Adjustment of the bias, provided by the source B4 effects adjustment of the total output'volts set up across the outputV impedance Z ofthe whole arrangement, i. e., this bias' Asource is Vvaried to control the value of volttageY amplitude which will be maintained sub-- stantially constant in the output impedance. In this Way constancy of output at a predetermined (and adjustable) value is obtained over a wide vrange of working frequencies.

`vWhere the invention is applied to a beat frequency oscillator of the usual kind comprising a variable oscillator and a xed tuned oscillator,

.an arrangement closely analogous to that just described and illustrated schematically in the accompanying Figure 2 is employed. In an application of this kind, the variable oscillator VO is a controlleddynatron or negative resistance oscillator, as above de scribed, and vits output is combined with the output from a fixed tuned oscillator FO -to produce a beat frequency which is fe-'d to a rectifier R' the rectied output being then lfed to Van amplifier, forv example, a low frequency amplifier LFA inthe case (to which the present invention is-very advantageously applied)fwhere.the beat frequency is a tone frequency. The voltage derived from the output ofthe amplifier LFA is fed to a control valve arrangement CV'consisting of a double-diode-triode as above described, which control valve is utilized to control the dynatron oscillatoralso as above described. The output circuit is represented by` OA. Obviously either or both ofthe component osv cillat'ors inthebeat frequency oscillator arrangement can be controlled as above described and/or made variable in frequency manually.v The resistanceRiin series with the tuned cir- Y cuit LiCi inA the rst -described embodiment is valve V1 is facilitated and a close approximation to linear operation more easily obtained. The control of the bias on the grid G2 of the doublediode-triode V2 is of great sensitivity because a1- though the diode and anodes are biased back the grid is left at normal potential and in these circumstances the double-diode-triode operates at a point on its characteristic where the mutual conductance is of normal value, i. e., relatively high.

Again the use of the resistance R2 connected between cathode K2 of the double-diode-triode and the heater H thereof to provide control E. M. F. for the dynatron also results in gain of sensitivity. Of course, the output may be controlled in ways other than that above described; f-or example, potentiometer control between output impedance Z and the control valve V2, i. e.Y

the double-diode-triode, may be resorted to, or the resistance R2 may be a potentiometer resistance whose movable tapping point is connected to the control valve circuit. The arrangement described, however, is preferred and with this said arrangement working on audio frequencies, it has been found possible to maintain a substantially constant output in spite of variations of the order of 40 decibels (i. e. variations in voltage amplication of about :1) in the amplification of the amplifier following the oscillator.

Although in the preceding description of the illustrated embodiments the use of a double-diodetriode has been referred to, (this arrangement gives great sensitivity) the invention is obviously not limited thereto, and fundamentally, any type of rectifier could be employed. Thus in broad essentials the arrangement of Figure l consists of four portions as represented by the four rectangles of the accompanying Figure 3, the first rectangle l representing any form of rectifier or rectifier and amplifier circuit providing the control E. M. F.; the rectangle 2 representing any form of controlled dynatron oscillator; the rectangle 3 representing an amplifier; and the rectangle ll representing an output circuit arrangement.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare that what I claim is:

In combination, a control oscillation generator comprising an electron discharge device having a cathode, an anode, a lscreen grid, and a control grid, and means for causing the emission of secondary electrons from said anode, resonant means in circuit with the anode and cathode for controlling the frequency of the oscillationsgener- NOL MEYER RUST. 

